I would suggest that your first electrical contractor is correct. In fact, he probably doesn't go far enough. Load test everything you can for at least 4 hours. You may want to take advantage of the heat generated by the load banks to test your HVAC system.
Once you are satisfied with the results of the load bank/thermal imaging testing, move on to operational testing and integrated systems testing (IST). Here are a few ideas;
1. Battery run-down test. Open the UPS input breaker while the UPS is at 100% rated capacity. Does the battery last as long as your UPS reseller told you it would? See IEEE testing standard 450 (wet cells) or IEEE 1189 (VRLAs)
2. UPS transfer tests. Transfer to UPS internal bypass while at rated capacity, transfer back. If you can do this with a transient recorder on the output of the UPS you should. Do the same with the external bypass if you have one.
3. Static transfer switches. If you have these as part of your infrastructure, transfer from Source 1 to Source 2 and back at rated capacity.
4. Generator and ATS tests. Simulate a utility failure. Watch the generator start and verify that the ATS switches to generator. Use a stopwatch, <10 seconds is good. This test will also reveal compatibility issues between the UPS and generator. These problems are common and the time to find out you have one is not during an actual utility failure. If you have the transient recorder hooked up, make sure that this test has no effect on the quality of power at the UPS output.
5. Get creative. What other events can you simulate that may actually occur IRL? Give your infrastructure a serious workout.
For many people, the success or failure of their business (and their career) depends on these systems operating as they should in an emergency. I say test them until you know that they are dependable.
Yes, this testing can be expensive. However, compare the cost of testing vs. the cost of one hour of unscheduled downtime. (If you don’t know what an hour of downtime will cost your company, you really should.)
One last thing, this is very specialized work and it may be a good idea to hire a professional commissioning agent. There are a number of good companies that can write testing procedures for you, perform the testing or both.
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